Instant Rage

Your rage begins at any time you wish, even when it's not your turn or when you're surprised. You can activate your rage as a reaction in response to an attack targeting you. Thus, you can gain the benefits of rage in time to prevent or ameliorate an undesirable event. For example, you can choose to enter a rage when an enemy attacks you, or casts a spell at you (to gain the benefits of a higher Constitution or your bonus on Will saves) before you know the results of the attack. You must be able to see the attack.